Method for Providing Composed Services in a Peer-To-Peer Network

1. A method for providing a service composed of subtasks in a peer-to-peer network, comprising: forming a first group by assigning a plurality of first peer devices of the peer-to-peer network to the first group, the first group being defined by a predetermined first subtask, each first peer device assigned to the first group configured to execute the predetermined first subtask; forming a second group by assigning a plurality of second peer devices of the network to the second group, the second group being defined by a predetermined second subtask, each second peer device assigned to the second group configured to execute the predetermined second subtask; publishing in the peer-to-peer network, by a peer device requesting a composed service, information relating to the requested composed service that identifies a sequence of subtasks to be executed for providing the composed service, the subtasks within the sequence of subtasks comprising the first and second predetermined subtasks such that the first predetermined subtask is to be performed prior to the second predetermined subtask when performing the sequence of subtasks to provide the requested composed service; selecting, by the peer device requesting the composed service, a second peer device from the second group, the selected second peer device being selected for executing the second subtask of the sequence of subtasks to provide the composed service; selecting, by the selected second peer device, a first peer device from the first group for executing the first subtask of the sequence of subtasks to provide the composed service after the selected second peer device is selected by the peer device requesting the composed service; executing the first subtask of the sequence of subtasks by the first peer device to provide the composed service; and executing the second subtask of the sequence of subtasks by the selected second peer device after the selected first peer device executes the first subtask to provide the composed service.

2. The method of claim 1 , further comprising: publishing a CandidateResource by each of the peer devices, the CandidateResource published by each peer device comprising information about subtasks which that peer device is configured to execute and a performance capability of that peer device; and publishing a SubtaskResource by the peer device requesting the composed service which comprises information about all the subtasks of the sequence of subtasks to be executed to provide the composed service and specifications for those subtasks.

3. The method of claim 1 , further comprising: defining a first watchdog peer device from the first group of peer devices; and monitoring, by the first watchdog peer device, a function of the selected first peer device executing the first subtask.

4. The method of claim 3 , comprising: the first watchdog peer device taking over execution of the first subtask when the selected first peer device fails.

5. The method of claim 1 , further comprising: publishing a ServiceGroupResource for the first group, the ServiceGroupResource comprising information about the first peer devices of the first group.

6. The method of claim 5 , wherein the ServiceGroupResource is periodically updated.

7. The method of claim 1 , wherein the sequence of subtasks comprises a third subtask and the method further comprising: forming a third group by assigning a plurality of third peer devices of the network to the third group, the third group being defined by a predetermined third subtask, each third peer device assigned to the third group configured to execute the predetermined third subtask; selecting, by the selected first peer device, a third peer device from the third group for executing the third subtask of the sequence of subtasks to provide the composed service after the selected first peer device is selected by the second peer device; and the selected third peer device executing the third subtask to provide the composed service prior to the selected first peer device executing the first subtask.

8. The method of claim 1 , wherein a ComposedServiceStateResource is published by the peer device requesting the composed service, the ComposedServiceStateResource comprising information identifying an operating state of the subtasks forming the composed service and/or intermediate results of the subtasks.

9. The method of claim 1 , comprising sending a first ring message from the peer device requesting the composed service to the selected first peer device which executes the first subtask first in the sequence of subtasks and the selected first peer device sending a second ring message to the selected second peer device; wherein the sending of the first and second ring messages are sent in order to instantiate the subtasks of the sequence of subtasks.

10. The method of claim 9 , wherein the first and second ring messages are sent at regular intervals to monitor execution of the composed service.

11. The method of claim 1 , further comprising: transmitting ring messages between the peer device requesting the composed service, the selected second peer device, the selected first peer device, and peer devices selected to perform other subtasks of the sequence of subtasks, each of the peer devices performing the subtasks of the sequence of subtasks determining an identification of the peer device which will execute an immediately subsequent subtask in the sequence of subtasks by reading a published ServiceGroupResource of the respective group defined by the immediately subsequent subtask.

12. The method of claim 1 , wherein the publishing in the peer-to-peer network, by the peer device requesting the composed service, information relating to the requested composed service that identifies the sequence of subtasks to be executed also identifies specifications of the peer devices to execute the subtasks.

13. The method of claim 1 , wherein the publishing in the peer-to-peer network, by the peer device requesting the composed service, information relating to the requested composed service that identifies the sequence of subtasks to be executed comprises: publishing a ComposedServiceResource comprising information about the sequence of the subtasks used for executing the composed service which is a criteria for the selection of executing peer devices that execute the subtasks of the sequence of subtasks, chaining of the subtasks of the sequence of subtasks, and execution parameters for the subtasks of the sequence of subtasks, wherein optional subtasks of the sequence of subtasks that are skippable in the execution of the chaining of the subtasks of the sequence of subtasks are indicated as being optional in the ComposedServiceResource.

14. The method of claim 13 , wherein the sequence of subtasks identifies a subtask that is skippable, the method also comprising: when all peer devices of a group defined by the optional subtask fail, skipping the skippable subtask.

15. The method of claim 1 , wherein at least one of the plurality of peer devices is assigned to several different groups defined by different predetermined subtasks.

16. The method of claim 1 , wherein the second predetermined subtask is a last subtask of the sequence of subtasks to be performed for providing the composed service.

17. A communication system, comprising: a plurality of peer devices communicatively connected to each other within a network, the peer devices comprising a first peer device, a second peer device, and a requesting peer device; the first peer device configured to execute a predetermined first subtask, the second peer device configured to execute a predetermined second subtask; the requesting peer device configured to request a composed service, the composed service comprising a sequence of subtasks comprising the first and second predetermined subtasks, the second predetermined subtask being a last subtask of the sequence of subtasks, and the first predetermined subtask of the sequence of subtasks being a subtask to be performed before the second predetermined subtask, the requesting peer device configured to request the composed service such that the requesting peer device selects the second peer device to perform the second predetermined subtask at a time the composed service is requested; and the second peer device configured to communicate with the first peer device to select the first peer device to perform the first subtask in response to the second peer device being selected by the requesting peer device to perform the second subtask of the sequence of subtasks.

18. The system of claim 17 , wherein the first peer device is configured to execute the first predetermined subtask to provide the composed service to the requesting peer device prior to the second peer device executing the second predetermined subtask to provide the composed service to the requesting peer device.

19. The system of claim 18 , wherein the requesting peer device is configured to send a first ring message to a peer device of the plurality of peer devices to perform a starting subtask of the sequence of subtasks and the first peer device is configured to send a second ring message to the second peer device to instantiate the subtasks of the sequence of subtasks.

20. The system of claim 17 , further comprising a first watchdog peer device configured to monitor a function of the first peer device when the first peer device executes the first subtask of the sequence of subtasks; and wherein: the sequence of subtasks comprises a third subtask that is to be executed prior to the first subtask and also prior to the second subtask; the plurality of peer devices also comprises a third peer device configured to execute the third subtask of the sequence of subtasks; and the first peer device is configured to communicate with the third peer device to select the third peer device to perform the third subtask of the sequence of subtasks in response to the first peer device being selected to perform the first subtask of the sequence of subtasks by the second peer device.